The main objective of this research is to determine Water Use Efficiency (WUE) of some major crops under farmer's management in the different region of Iran including Kerman, Hamedan, Moghan, Golestan and Khuzestan provinces. The research also attempted to assess and identify the sources of inefficiencies in improving WUE. Based on methodology, WUE was determined by measuring crop yield (Kg) and gross water used (m3). Based on results, the average WUE for the Wheat (grain), Sugar beet (root), Potato, Silage Corn, Cotton, Alfalfa (dry weight basis), Barley (grain), Chickpea (irrigated) and Sugarcane (Cane) was 0.73, 4.56, 2.18, 5.58, 0.71, 1.46, 0.56, 0.18 and 2.94 Kg/m3, respectively. Using the measured WUEs and cropping areas of the different crops in the different regions, the country’s weighted average WUE was estimated to be 1.38 Kg/m3.